Cutting blades for cutting gears and the like may be of many forms. One form widely used are cutting blades known as "stick blades" which are made from a length of material such as bar stock.
One example of cutting blades of the bar stock type are those blades known as "profile sharpened" blades. In these blades, the top surface, side profile surfaces, and, the cutting face (in some types), are ground to restore and resharpen the blades. In those types of blades not requiring sharpening of the front face, metallurgical coatings or other treatments which improve cutting and wear characteristics are usually included on the front face. Profile-sharpened cutting blades may be used to remove stock material from the outside or concave flank of a tooth slot (outside blade), the inside or convex flank of a tooth slot (inside blade), and/or the bottom portion of the tooth slot (bottom blade).
One type of profile-sharpened cutting blade that does not require the front face to undergo grinding during sharpening is disclosed in U.S. Pat. No. 4,260,299 to Ryan et al., this cutting blade comprises a base portion and a cutting end with the cutting end having a front rake surface arranged at a particular rake angle, a back face, top surface, cutting profile surface and clearance profile surface. The cutting and clearance edges are defined by the intersection of the front rake surface with the cutting profile surface and the clearance profile surface, respectively.
Another known type of profile-sharpened cutting blade not requiring the front face to be ground during sharpening is shown in U.S. Pat. No. 4,575,285 to Blakesley. This blade also comprises a base portion and cutting end. The cutting end includes a front rake surface, a back face, opposing side surfaces, top surface, and opposing cutting and clearance profile surfaces which at their intersection with the front rake surface form, respectively, cutting and clearance edges. The cutting blade further includes a slot extending the length of the blade through the front rake surface and intersecting the clearance profile surface which intersection forms a second cutting edge. This second cutting edge removes metal from the side of a tooth slot opposite the side being cut by the cutting edge formed on the cutting profile surface.
Yet another type of profile-sharpened cutting blade not requiring the front face to be ground during sharpening is disclosed in commonly assigned, copending application Ser. No. 036,312 to Blakesley et al. The cutting blade comprises a generally uniform cross-section along its length and includes opposite end surfaces, a pair of opposed side surfaces, a back surface, and a front surface. The front surface includes a pair of mounting surfaces, a front rake surface, and a connecting surface. The front rake surface and the connecting surface are located between the mounting surfaces. The front rake surface extends from one of the pair of mounting surfaces and is oriented at a rake angle with respect thereto. The connecting surface extends from the other of the pair of mounting surfaces to the rake surface and intersects therewith.
The cutting blade includes a pressure side surface (also known as a cutting profile surface), a clearance side surface, and a top surface. The pressure side surface is oriented at a predetermined pressure angle with respect to a side surface and a cutting edge is defined by the intersection of the pressure side surface and the front surface. The clearance side surface is oriented at a predetermined clearance angle with respect to a side surface and a clearance edge is defined by the intersection of the clearance side surface and the front surface.
U.S. Pat. No. 4,265,053 to Kotthaus discloses form-ground profile-sharpened cutting blades of the type wherein along with the top surface and side profile surfaces, the front face also requires grinding during sharpening. The sharpening procedure employs three grinding discs each sharpening one of the inner profile surface, the outer profile surface, and the front face of the cutting blade.
A method of sharpening cutting blades having only top and side profile surfaces that require resharpening by utilizing a single grinding wheel to form grind the profile surfaces is disclosed in U.S. Pat. No. 4,144,678 to Ellwanger et al. and in Pedersen et al., "Precision Profile Grinding for High Production", SME 1982 International Tool & Manufacturing Engineering Conference, May 17-20, 1982, MR82-246.
U.S. Pat. No. 5,168,661 to Pedersen et al. teaches a method of sharpening profile-sharpened cutting blades by contour grinding the top and side profile surfaces on the blades by relative motion between the cutting blade and the grinding wheel.
In the stick-type cutting blades discussed above, generally those utilized as inside or outside blades, it is also known to include on the cutting profile surface, a protuberant portion adjacent the top surface and extending from the front rake surface to the back face. The protuberant portion is formed as a reduction in blade pressure angle for the purpose of creating an undercut when cutting gears, particularly pinion gears, in order to eliminate interference when running with their mating gear, such as during lapping or when in actual use.
In some contour-type sharpening processes for stick type cutting blades having this protuberant portion, it has been noticed that subsequent to final grinding of the cutting (pressure) profile surface, a hole or divot is present on the protuberant portion of the cutting edge at a point adjacent to its intersection with the cutting profile surface. The cause of this hole is believed to be due to the difference between the considerable amount of grinding force that is required when traversing the relatively large area of the cutting profile surface as opposed to the significantly smaller amount of grinding force that is utilized to commence grinding the relatively small area of the protuberant portion surface. The hole or divot on the cutting edge will be discussed in greater detail below.
The hole or divot may be reduced with slower feed rates during grinding of the cutting blade, however, any appreciable reduction in size of the hole requires increasing grinding time by about a factor of four which is unacceptable from a production standpoint.
It is an object of the present invention to provide a process in which profile-sharpened stick-type cutting blades of the types discussed above may be ground without the formation of a hole or divot in the cutting edge at the intersection of the cutting profile surface and the protuberant portion.
It is an object of the present invention to provide a sharpening process for profile-sharpened stick type cutting blades wherein the hole or divot is eliminated without a significant increase in length of process time.
It is another object of the present invention to grind stick-type cutting blades having no protuberant portion by the inventive process.
It is a further object of the present invention to provide stick-type cutting blades having a cutting profile surface ground in accordance with the present inventive process.